Connector contact fingers are used in test rigs in the semi-conductor industry to test integrated circuit (IC) packages. A typical connector, as shown in FIGS. 1 and 6, comprises a retainer wherein a plurality of parallel metallic strips are mounted. The retainer (103), is a rectangular block typically made from non-conducting material such as moulded plastic wherein one longitudinal edge has been moulded into a rectangular-shaped recess (reference numeral 104 of FIG. 6). The metallic strips are embedded in the retainer, such that the two ends of the strips are exposed and available for electrical connections. One end of the strips (101), protrudes out from the retainer, and is known as the fingers end, with each exposed strip representing one finger. The second end of the metal strips (102), protrudes across but within the recess , and is known as the leg end, with each exposed strip from the second end representing one leg. Small outline surface-mount packaging for integrated circuits (SOIC's) is a widely used basic package-mounting technique in the semi-conductor industry.
An example is the SOP (small outline packages) having leads that protrude out from the packaging in a gull-wing formation (reference numeral 203 of FIG. 2). The gull-wing lead of an SOIC package consists of a flat wing-tip section (201), and a bent wing-centre section (202). A typical instrument for testing the aforementioned IC packages is called a testing rig, wherein the connector contact fingers is mounted onto the contactor assembly. The contactor assembly, as shown in FIG. 3, comprises a main track in the centre (reference numeral 301) whereon the IC device to be tested would be transferred A pair of connectors are installed on the right side of the main track (303), and a second pair on the left side (302) of the main track. Each pair of connectors consists of one top connector in the inverted position, and one bottom connector in the upright position. Installation of the connectors involves first positioning an IC package (203) onto the designated position on the main track between the two pairs of connectors as shown in FIG. 4. Then the position of each connector is adjusted whereby each finger is aligned with the corresponding lead. Once precise alignment is achieved, devices to be tested are transferred sequentially through the main track. When the device to be tested stops at the designated position on the main track, the two pairs of connectors act like two pairs of pincers, and clamp onto the corresponding leads of the device. Once connection is made, current will flow through the device, and the function of the device can be tested. If the pre-set current level is measured, the device is accepted, if the pre-current level is not detected, the device is rejected as defective.
Precise alignment involves adjustment in the X position in the direction of the device flow (as shown by the double-headed arrow of reference numeral 401), and the Y position at 90.degree. to the device flow (402) as shown in FIG. 4. Movement in the Z position vertically (reference numeral 502 of FIG. 5) is used to achieve the clamping function. The correct alignment in the X-direction would result in the lead (201) being located at the centre of both the top and bottom (101) fingers as shown in reference numeral 404 of FIGS. 4B and 4D. An incorrect alignment in the direction would cause the lead to be located off to one side of the top or the bottom fingers, resulting in poor contact, as shown in 403 of FIGS. 4A and 4C. Correct alignment in the Y-direction (502) would allow the fingers to clamp at the central portion of the wing-tip of the lead, giving good contact as shown in 501 of FIG. 5A. Incorrect alignment in the Y-direction by positioning the connector too close to the main track results in the fingers clamping onto the wing-centre, causing poor contact and damage to the lead, as shown in 503 of FIG. 5B. Conversely, positioning the connector too far away from the main track results in the fingers clamping the lead toward the tip of the gull-wing, again causing poor contact.
The leg area of the connector comprises a plurality of parallel legs protruding across but within the recess of the retainer. The space between the legs and the retainer, as shown in reference numeral 104 of FIGS. 6 and 6A, functions as a socket wherein the card edge (601) of a flexible printed circuit board (602) can be inserted. Once the flexible printed circuit board is properly connected and the connectors are precisely aligned, testing of the devices may commence.
Although the aforementioned method is widely accepted for testing IC devices, it has several problems that render the process inefficient and difficult. The first problem is that the area of contact between the fingers and the device lead is extremely small. As each finger converges onto the lead at an angled finger tip as shown in reference numeral 204 of FIG. 2, the line of contact is essentially the edge of the metal strip of the finger. If the lead is not precisely aligned as described above, poor contact and faulty connection would result, giving faulty readings. As a result, precise alignment by a skilled technician is required every time a connector is changed. This alignment procedure is tedious and time-consuming.
Another difficulty is encountered when force is applied in the Z-direction to raise the lower connectors in order to clamp the device leads between the top and bottom fingers. Finding the appropriate contact pressure is very important in ensuring long life to the contact leads and fingers. Too much force would cause excessive flexing and the result is broken or bent contact leads or fingers. Too little force might result in faulty connection at the lines of contact. Even when the correct pressure is used, extended usage results in a co-planarity problem whereby one or more fingers within the same connector become bent or flexed. In this instance, the bent fingers would not be lying on the same plane as the other fingers of the same connector. As a result, the bent fingers cannot establish contact with the corresponding device leads. If misalignment or co-planarity problems occur, a device which would have passed the test if proper connections were made, may actually be rejected due to faulty readings caused by poor contacts. This raises the rejection rate in the quality control process, and is very costly to the industry.
Contact between the flexible printed circuit board and the legs of the connector is also problematic. As shown in FIG. 6, there is no special design in the art whereby the card edge of the flexible printed circuit board can be secured onto the connector. Proper connection is dependent on the spring force exerted by the legs on the card edge. The connector is shifted along the Z axis to clamp each new IC device as each device is being tested. Such shifting movement could cause the card edge to come loose from the recess of the connector, resulting in poor contact with the legs. In addition, a vertical movement could cause the flexible printed circuit board to tilt and impinge upon the legs, deflecting some or all the legs out of their normal position, resulting in further co-planarity problem at the leg end or a loss of spring force. The consequence of the above problems is that as one increases the number of tests conducted using the same set of connectors, the rejection rate also increases due to poor contact. Limiting the number of tests conducted for each set of connectors would improve the fidelity of the tests. However this is not taught in the art, as each change of connectors requires time-consuming re-alignment, slowing down the quality control process.